Liquid level indicating means

ABSTRACT

A closed fuel tank comprises a liquid level indicating means having a transducer cell mounted adjacent the bottom thereof. The cell comprises a bottom wall having a centrally disposed opening formed therein to communicate fuel to an internal, air-filled chamber of the cell. A tube forms an extension of the opening and extends downwardly from the bottom wall to form a &#39;&#39;&#39;&#39;bubble trap.&#39;&#39;&#39;&#39; A perforated baffle member encapsulates the tube to retard ingress of fuel into the chamber to prevent pressure surges therein. The air pressure level in the cell, proportional to the head of fuel in the tank, is communicated to a calibrated fuel gage mounted externally of the tank.

H1 ite ttes Barbee 1 Apr. 10, 1973 [52] US. Cl ..73/299, 73/392 [51]Int. Cl ..G01f 23/14 [58] Field of Search ..73/299, 302, 392

[56] References Cited UNITED STATES PATENTS 827,318 7/1906 Martin..73/302 1,646,957 10/ 1927 Eynon ..73/299 1,055,099 3/ 1913 Sullivan..73/299 1,646,311 l0/l927 Page ..73/299 FOREIGN PATENTS OR APPLICATIONS653,316 3/1929 France ..73/299 3/1947 Great Britain ..73/299 9/1947Italy ..73/299 Primary Examiner-S. Clement Swisher AssistantExaminerDenis E. Corr Attorney-Fryer, Tjensvold, Feix, Phillips & Lempio[57] ABSTRACT A closed fuel tank comprises a liquid level indicatingmeans having a transducer cell mounted adjacent the bottom thereof. Thecell comprises a bottom wall having a centrally disposed opening formedtherein to communicate fuel to an internal, air-filled chamber of thecell. A tube forms an extension of the opening and extends downwardlyfrom the bottom wall to form a bubble trap. A perforated baffle memberencapsulates the tube to retard ingress of fuel into the chamber toprevent pressure surges therein. The air pressure level in the cell,proportional to the head of fuel in the tank, is communicated to acalibrated fuel gage mounted externally of the tank.

11 Claims, 5 Drawing Figures PATENTED m1 0197s INVENTOR GA I L BARBEE j#:ay 7 I I ATTORNEYS LIQUID LEVEL INDICATING MEANS BACKGROUND OF THEINVENTION This invention relates to liquid level indicating meanscomprising a transducer cell and sending unit for translating the headof liquid in a tank to an air pressure signal and for transmitting sameto a pressure and fuel gage.

A number of conventional fuel level indicating devices utilize a trappedair system for indicating the level of fuel contained in a fuel tank.Such system normally constitutes a cell, in the form of an invertedcontainer having a completely open bottom, which is mounted within thetank. As the fuel level rises, the pressure of air trapped in the cellincreases a proportional amount to generate a pressure signal which istransmitted to a calibrated pressure gage.

Mobile vehicles, such as earth working equipment, frequently operate onuneven terrain, side slopes, hills, etc., causing their fuel tanks totilt relative to ground level. When such tilting becomes excessive, theconventional opened bottom cell permits trapped air to escape therefrom.Fuel thereafter replaces the displaced air when the vehicle returns toits normal level position. Such an interchange functions to transmit afalse reading to the fuel gage to induce the vehicle to run out of fuelduring an earth working operation.

Another problem encountered with the opened bottom type of cell is oneoccasioned due to side-to-side sloshing of fuel in the tank,particularly when the tank is near empty. Such sloshing generatespressure surges of high magnitude which tend to damage delicatemechanisms employed in the pressure gage and effect an erratic readingthereon.

SUMMARY AND OBJECTS OF THE INVENTION An object of this invention is toovercome the above, briefly described problems by providing aneconomical and highly accurate liquid level indicating means for tanks,which is substantially insensitive to pronounced tipping of the tankrelative to ground level and to sloshing of the fuel therein.

The indicating means comprises a transducer cell adapted to be attachedadjacent the bottom of a fuel tank or the like. A relatively smallopening is formed through a bottom wall of the transducer and spaced asubstantial distance from sidewalls thereof to communicate the head ofliquid fuel to an air-conditioning chamber of the transducer. Variationsin such head will in turn vary the air pressure in the transducer whichis reflected on a fuel gage. In the preferred embodiment, a tube formsan extension of the opening and bafi'le means encapsulate the tube todampen pressure surges therearound.

BRIEF DESCRIPTION OF THE DRAWINGS Other objects of this invention willbecome apparent from the following description and accompanying drawingswherein:

FIG. 1 is a side elevational view of a tank which is sectioned to exposea liquid level indicating means embodiment of this invention operativelyassociated therewith;

FIG. 2 is an enlarged, cross-sectional view of a transducer cellemployed in the indicating means;

FIG. 3 is a partial, bottom plan view of the transducer cell, taken inthe direction of arrows III-III in FIG. 2;

FIG. 4 is a view similar to FIG. 2, but showing the transducer cell in atilted position relative to ground level; and

FIG. 5 is a view illustrating a prior art cell in a corresponding tiltedposition.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1-3 illustrate apreferred liquid level indicating means embodiment of this invention,attached to a conventional tank 10 defining a closed chamber thereinadapted to contain a liquid such as diesel fuel. The indicating meanscomprises a sending unit or transducer cell 1 1 suitably mounted on asidewall of the tank and near the bottom thereof. The transducer cell isoperatively connected to an extemally-mounted pressure gage means 12 bya conduit 13 extending from the top of the transducer to the top of thetank and an extension conduit 14 positioned externally of the tank.

The transducer cell comprises a substantially closed housing formed bysuitably connected top, side and bottom walls 15-17, respectively. Thehousing, when viewed in top-plan, is preferably circular although othershapes such as rectangular (e.g., square) could be employed therefor.The housing defines an air chamber 18 therein which has a predeterminedvolume substantially less than that of tank 10.

A tube 19, preferably cylindrical, is attached to and forms an extensionof an opening 20 formed through bottom wall or plate 17. The opening isspaced at a substantial distance from the sidewalls and is preferablycentrally located on the bottom wall. The area of the opening issubstantially less than the area of the bottom plate (e.g.,approximately 1:10) with the opening illustrated having an area whichapproximates l 1.5 percent of the area of the bottom wall.

A cylindrical, perforated cap 21, secured to the bottom wall,encapsulates the tube. A typical array of perforations 22 is illustratedin FIG. 3. The cap functions as a baffle means to dampen pressure surgestherearound as will be hereinafter described.

Typically, tank 10 is filled with a liquid fuel, such as gasoline ordiesel fuel, by removing a cap 23 from a filler spout 24 connected tothe top of the tank. As the fuel level rises around the transducer cell,fuel passes through perforated cap 21, but will not enter chamber 18 dueto the air trapped therein. As the fuel level continues to rise, the airpressure in chamber 18 and conduits l3 and 14 rises a proportionateamount to indicate same on calibrated pressure and fuel gage 12.

In the case of diesel fuel, commonly used in engines I employed on largeearthmoving vehicles, the air pressure will increase approximatelyone-half ounce per square inch for each inch of rise of the fuel head.Thus, if a fuel tank 50 inches deep is completely filled with dieselfuel, the air pressure in chamber 18 and conduits l3 and 14 would beapproximately 25 ounces per square inch. Since the depth of the fueltank will usually vary with the size of the vehicle, the gages willnecessarily be calibrated accordingly. However, identical transducercells 11 can be used in connection with all such tanks regardless oftheir depth.

FIG. 4 shows a near-empty tank in a tilted position wherein bottom plate17 of the transducer cell, for example, is at a tilt angle a relative toa horizontal plane or ground level 1-1. Such tilting normally occurswhen a vehicle is operated on a grade or side slope. When the 5 tank istilted to the position shown, a negligible amount of air has alreadyleaked past point P and has been replaced in tube 19 by a like volume offuel. So long as point P remains vertically below point P,, fuel will beprevented from entering chamber 18.

Tube 19 and opening 21 thus cooperate to function as a bubble trap toprevent air from escaping from chamber 18 to distort the reading on gage12. The small volume of air-replaced-by-fuel in the tube is too minuteto affect the calibration of the gage. Tube 19 is constructed anddimensioned so that the volume of air in chamber 18 remains intact whenthe vehicle is operated on side slopes or grades which can be safelynegotiated.

Such dimensions, when applied to a tube having a circular cross-section,may be calculated in accordance with the formula a Arc Tan (LID). Insuch formula, a,,,,, equals the maximum tilt angle (FIG. 4) at which thevehicle can be safely operated and L and D equal the length and innerdiameter, respectively, of the tube. The angle a also defines themaximum angle (a in FIG. 4) at which bottom wall 17 can be tippedrelative to horizontal plane H without permitting liquid in tank fromentering air chamber 18.

For example, the FIGS. 1-4 tube is dimensioned so that angle a, equals45. In accordance therewith, point P, will remain below point P, so longas the tank is not tilted beyond 45 relative to ground level H, to

prevent the ingress of fuel into chamber 18. Should the tank be tiltedinadvertently beyond the 45 inclination, to allow air to escape fromchamber 18 and to allow the ingress of fuel therein, the fuel can beeasily drained from the chamber simultaneously along with a draining ofthe fuel tank.

FIG. 5 illustrates a prior art, open bottom type of cell 11a which hasbeen tilted to the same degree as cell 11 in FIG. 4. As a tank 10a istilted, the air from a chamber 18a of the cell escapes at point P and isreplaced by fuel. Comparing the two figures, it can be readily seen thata substantial volume of fuel enters the prior art cell under identicaltilt angles. When tank 10a is returned to a level position, the fuelwill remain in the cell to induce a false reading on a fuel gage (notshown) attached to a sensing conduit 13a.

A primary function of perforated cap member or baffle means 21 is toinhibit the sloshing effect of the fuel around opening 20, particularlywhen the fuel tank is near empty. Thus, pressure surges are damped andminimized and damage to the gage is prevented. Also, the damping of suchpressure surges by the baffle means will stabilize the needle of gage 12which might otherwise fluctuate rapidly to provide an erratic read- Gage12 (FIG. 1) may have its needle 25 function as a normally open switchwhich closes on a contact 26 to provide means for visually indicatingwhen the needle closely approaches the empty (E) reading. Closing of theswitch completes an electrical circuit to light a bulb 27 located on thevehicles dashboard (not shown) to alert the operator prior to stallingof the vehicle.

It should be understood that tube 19 and/or baffle means 21, althoughpreferred, could be eliminated from the indicating means in certainapplications. Opening 20 would still function to provide a much moreaccurate reading on gage 12 than would the FIG. 5 prior art system. Inparticular, although some fuel would enter chamber 18 when it assumesthe FIG. 4 position, the volume thereof would be substantially less thanthe volume of fuel contained in chamber 18a of the FIG. 5 conventionalcell.

What is claimed is:

1. A liquid level indicating means adapted for use with a closed tankcomprising a transducer cell having connected top, bottom, and

side walls defining an air chamber of predetermined volume therein,

means forming an opening through said bottom wall which is spaced asubstantial distance from said side walls and has an area substantiallyless than the area of said bottom wall,

gage means operatively connected to said transducer cell for sensing andindicating variable air pressure levels in said air chamber and bafi'lemeans, comprising a perforated cap, attached exteriorly on said bottomwall to completely cover said opening to dampen pressure surges ofliquid thereat.

2. The invention of claim 1 further comprising a tank defining a liquidchamber therein having a volume substantially greater than said airchamber, said transducer cell mounted in said liquid chamber adjacent toa bottom of said tank and said gage means positioned externally of saidtank whereby the variable air pressure indicated by said gage means isresponsive to the head of liquid contained in said liquid chamber.

3. The invention of claim 2 further comprisingmeans operativelyconnected to said gage means for visually indicating when the liquid insaid tank falls below a predetermined level.

4. The invention of claim 3 wherein said means operatively connected tosaid gage means comprises an electrical circuit having a movable needleof saidgage means forming a normally open switch thereof.

5. The invention of claim 1 further comprising a tube attached to andextending away from said bottom wall to form an extension of saidopening.

6. The invention of claim 5 wherein saidtube is cylindrical and isconstructed in accordance with the formula a Arc Tan (L/D) wherein:

a,,,,, The maximum angle at which said bottom wall of said transducercell can be tipped relative to a horizontally disposed plane withoutpermitting a liquid in said tank from entering the air chamber of saidtransducer cell;

L The vertical length of said tube; and

D The inner diameter of said tube.

7. The invention of claim 6 wherein a is no greater than approximately45.

8. The invention of claim 1 further comprising a tube attached to andextending away from said bottom wall to form an extension of saidopening, said baffle means encapsulating said tube.

9. The invention of claim 1 wherein said opening has an areaapproximating one-tenth of the area of said bottom wall.

the area of said bottom wall,

gage means operatively connected to said transducer cell for sensing andindicating variable air pressure levels in said air chamber;

baffle means attached exteriorly on said bottom wall to completely coversaid opening to dampen pressure surges of liquid thereat and a tubeattached to and extending away from said bottom wall to form anextension of said opening, said baffle means encapsulating said tube.

1. A liquid level indicating means adapted for use with a closed tankcomprising a transducer cell having connected top, bottom, and sidewalls defining an air chamber of predetermined volume therein, meansforming an opening through said bottom wall which is spaced asubstantial distance from said Side walls and has an area substantiallyless than the area of said bottom wall, gage means operatively connectedto said transducer cell for sensing and indicating variable air pressurelevels in said air chamber and baffle means, comprising a perforatedcap, attached exteriorly on said bottom wall to completely cover saidopening to dampen pressure surges of liquid thereat.
 2. The invention ofclaim 1 further comprising a tank defining a liquid chamber thereinhaving a volume substantially greater than said air chamber, saidtransducer cell mounted in said liquid chamber adjacent to a bottom ofsaid tank and said gage means positioned externally of said tank wherebythe variable air pressure indicated by said gage means is responsive tothe head of liquid contained in said liquid chamber.
 3. The invention ofclaim 2 further comprising means operatively connected to said gagemeans for visually indicating when the liquid in said tank falls below apredetermined level.
 4. The invention of claim 3 wherein said meansoperatively connected to said gage means comprises an electrical circuithaving a movable needle of said gage means forming a normally openswitch thereof.
 5. The invention of claim 1 further comprising a tubeattached to and extending away from said bottom wall to form anextension of said opening.
 6. The invention of claim 5 wherein said tubeis cylindrical and is constructed in accordance with the formula amaxArc Tan (L/D) wherein: amax The maximum angle at which said bottom wallof said transducer cell can be tipped relative to a horizontallydisposed plane without permitting a liquid in said tank from enteringthe air chamber of said transducer cell; L The vertical length of saidtube; and D The inner diameter of said tube.
 7. The invention of claim 6wherein amax is no greater than approximately 45*.
 8. The invention ofclaim 1 further comprising a tube attached to and extending away fromsaid bottom wall to form an extension of said opening, said baffle meansencapsulating said tube.
 9. The invention of claim 1 wherein saidopening has an area approximating one-tenth of the area of said bottomwall.
 10. The invention of claim 1 wherein said opening is at leastapproximately located at the center of said bottom wall.
 11. A liquidlevel indicating means adapted for use with a closed tank comprising atransducer cell having connected top, bottom, and side walls defining anair chamber of predetermined volume therein, means forming an openingthrough said bottom wall which is spaced a substantial distance fromsaid side walls and has an area substantially less than the area of saidbottom wall, gage means operatively connected to said transducer cellfor sensing and indicating variable air pressure levels in said airchamber; baffle means attached exteriorly on said bottom wall tocompletely cover said opening to dampen pressure surges of liquidthereat and a tube attached to and extending away from said bottom wallto form an extension of said opening, said baffle means encapsulatingsaid tube.